1. Field of the Invention
This invention relates to a method and an apparatus for inserting a watermark into contents information. In addition, this invention relates to a method and an apparatus for extracting a watermark from watermarked contents information.
2. Description of the Related Art
U.S. Pat. No. 5,930,369 (corresponding to Japanese published unexamined patent application 9-191394) discloses digital watermarking of audio, image, video or multimedia data which is achieved by inserting the watermark into the perceptually significant components of a decomposition of the data in a manner so as to be visually imperceptible. Specifically, U.S. Pat. No. 5,930,369 discloses a method in which a frequency spectral image of the data, preferably a Fourier transform of the data, is obtained, and a watermark is inserted into perceptually significant components of the frequency spectral image. The resultant watermarked spectral image is subjected to an inverse transform to produce watermarked data. The watermark is extracted from watermarked data by first comparing the watermarked data with the original data to obtain an extracted watermark. Then, the original watermark, original data and the extracted watermark are compared to generate a watermark which is analyzed for authenticity of the watermark.
In U.S. Pat. No. 5,930,369, the Fourier transform and the inverse transform cause a reduction in the cost performance ratio of the method.
H. Ogawa et al., xe2x80x9cA Copying Information Embedding Method using DCT for Digital Moviesxe2x80x9d, in SCIS""97-31G, have reported watermarking methods which are suitable for MPEG bit streams. The methods are based on modifying DCT coefficients, motion vectors, and quantizer matrices.
It is assumed that data which have been watermarked by one of the methods reported by H. Ogawa et al. are subjected to affine transformation to slightly rotate or distort a picture. It tends to be difficult to accurately extract the watermark from the transformation-resultant watermarked data.
International patent application WO 89/08915 discloses a method of inserting an identification string into a digital audio signal by substituting the xe2x80x9cinsignificantxe2x80x9d bits of randomly selected audio samples with the bits of an identification code. The method in application WO 89/08915 can also be applied to coding schemes which do not have a defined word structure, such as delta modulation, in which case digits can be replaced completely randomly without regard to relative significance.
In the case of access to a portion of a digital audio signal into which an identification string has been inserted by the method in application WO 89/08915, it is difficult to recover (reproduce) the whole of the identification string if at least part of the identification string is in another portion of the digital audio signal.
It is a first object of this invention to provide an improved method of inserting a watermark into contents information.
It is a second object of this invention to provide an improved apparatus for inserting a watermark into contents information.
It is a third object of this invention to provide an improved method of extracting a watermark from watermarked contents information.
It is a fourth object of this invention to provide an improved apparatus for extracting a watermark from watermarked contents information.
A first aspect of this invention provides a method of inserting watermark information into digital data. The method comprises the steps of determining a specified data value in response to the watermark information; and changing a data-value occurrence-frequency distribution of a predetermined number of samples of the digital data into a modified occurrence-frequency distribution in which the specified data value occurs at a frequency extremely different from frequencies of occurrence of data values other than the specified data value.
A second aspect of this invention provides a method of inserting watermark information into digital data. The method comprises the steps of calculating differences between samples of the digital data to generate difference data representing the calculated differences; determining a specified difference data value in response to the watermark information; and changing a data-value occurrence-frequency distribution of a predetermined number of samples of the difference data into a modified occurrence-frequency distribution in which the specified difference data value occurs at a frequency extremely different from frequencies of occurrence of difference data values other than the specified difference data value.
A third aspect of this invention provides a method of inserting watermark information into digital data. The method comprises the steps of calculating differences between samples of the digital data to generate difference data representing the calculated differences; determining a specified difference data value in response to the watermark information; and changing a normalized data-value occurrence-frequency Laplace distribution of a predetermined number of samples of the difference data into a modified occurrence-frequency distribution in which the specified difference data value occurs at a frequency extremely different from frequencies of occurrence of difference data values other than the specified difference data value.
A fourth aspect of this invention provides a method of extracting watermark information from digital data. The method comprises the steps of detecting an occurrence-frequency distribution of data values in a predetermined number of samples of the digital data; detecting, from the detected occurrence-frequency distribution, a data value which occurs at a frequency extremely different from frequencies of occurrence of other data values; and reproducing the watermark information on the basis of the detected data value.
A fifth aspect of this invention provides a method of extracting watermark information from digital data. The method comprises the steps of calculating differences between samples of the digital data to generate difference data representing the calculated differences; detecting an occurrence-frequency distribution of difference data values in a predetermined number of samples of the difference data; detecting, from the detected occurrence-frequency distribution, a difference data value which occurs at a frequency extremely different from frequencies of occurrence of other difference data values; and reproducing the watermark information on the basis of the detected difference data value.
A sixth aspect of this invention provides a method of extracting watermark information from digital data. The method comprises the steps of calculating differences between samples of the digital data to generate difference data representing the calculated differences; detecting a normalized occurrence-frequency Laplace distribution of difference data values in a predetermined number of samples of the difference data; detecting, from the detected normalized occurrence-frequency Laplace distribution, a difference data value which occurs at a frequency extremely different from frequencies of occurrence of other difference data values; and reproducing the watermark information on the basis of the detected difference data value.
A seventh aspect of this invention provides an apparatus for inserting watermark information into digital data. The apparatus comprises means for determining a specified data value in response to the watermark information; and means for changing a data-value occurrence-frequency distribution of a predetermined number of samples of the digital data into a modified occurrence-frequency distribution in which the specified data value occurs at a frequency extremely different from frequencies of occurrence of data values other than the specified data value.
An eighth aspect of this invention provides an apparatus for inserting watermark information into digital data. The apparatus comprises means for calculating differences between samples of the digital data to generate difference data representing the calculated differences; means for determining a specified difference data value in response to the watermark information; and means for changing a data-value occurrence-frequency distribution of a predetermined number of samples of the difference data into a modified occurrence-frequency distribution in which the specified difference data value occurs at a frequency extremely different from frequencies of occurrence of difference data values other than the specified difference data value.
A ninth aspect of this invention provides an apparatus for inserting watermark information into digital data. The apparatus comprises means for calculating differences between samples of the digital data to generate difference data representing the calculated differences; means for determining a specified difference data value in response to the watermark information; and means for changing a normalized data-value occurrence-frequency Laplace distribution of a predetermined number of samples of the difference data into a modified occurrence-frequency distribution in which the specified difference data value occurs at a frequency extremely different from frequencies of occurrence of difference data values other than the specified difference data value.
A tenth aspect of this invention provides an apparatus for extracting watermark information from digital data. The apparatus comprises means for detecting an occurrence-frequency distribution of data values in a predetermined number of samples of the digital data; means for detecting, from the detected occurrence-frequency distribution, a data value which occurs at a frequency extremely different from frequencies of occurrence of other data values; and means for reproducing the watermark information on the basis of the detected data value.
An eleventh aspect of this invention provides an apparatus for extracting watermark information from digital data. The apparatus comprises means for calculating differences between samples of the digital data to generate difference data representing the calculated differences; means for detecting an occurrence-frequency distribution of difference data values in a predetermined number of samples of the difference data; means for detecting, from the detected occurrence-frequency distribution, a difference data value which occurs at a frequency extremely different from frequencies of occurrence of other difference data values; and means for reproducing the watermark information on the basis of the detected difference data value.
A twelfth aspect of this invention provides an apparatus for extracting watermark information from digital data. The apparatus comprises means for calculating differences between samples of the digital data to generate difference data representing the calculated differences; means for detecting a normalized occurrence-frequency Laplace distribution of difference data values in a predetermined number of samples of the difference data; means for detecting, from the detected normalized occurrence-frequency Laplace distribution, a difference data value which occurs at a frequency extremely different from frequencies of occurrence of other difference data values; and means for reproducing the watermark information on the basis of the detected difference data value.
A thirteenth aspect of this invention provides an apparatus for inserting watermark information into digital data. The apparatus comprises means for deriving differences between samples of the digital data; means for selecting at least one from among values, which differences between samples of the digital data can take, as a forbidden value in response to the watermark information; means for deciding whether or not the derived differences are equal to the forbidden value; and means for changing logic states of samples of the digital data which relate to the derived differences decided to be equal to the forbidden value to convert the digital data into conversion-resultant data to inhibit differences between samples of the conversion-resultant data from taking the forbidden value.
A fourteenth aspect of this invention provides an apparatus for extracting watermark information from digital data. The apparatus comprises means for deriving differences between samples of the digital data; means for detecting an occurrence-frequency distribution of values of the derived differences; means for comparing the detected occurrence-frequency distribution with a predetermined reference occurrence-frequency distribution to find a difference value whose detected occurrence frequency is smaller than its reference occurrence frequency by more than a given percentage; and means for reproducing the watermark information on the basis of the found difference value.